Forced-convection heat exchanger for a rotary electrical machine

ABSTRACT

A forced-convection heat exchanger for a rotary electrical machine, the particularity of which is the fact that it comprises one or more tubing elements arranged between the conductors that constitute the stator windings of said rotary electrical machine, a cooling fluid circulating into said tubing elements.

[0001] The present invention relates to a forced-convection heat exchanger for rotary electrical machines. More particularly, the invention relates to forced-convection heat exchanger of the compact type for a rotary electrical machine such as for example an electric motor. Rotary electrical machines are traditionally plagued by significant losses due to the Joule effect in the stator elements (copper and iron) and due to the viscous friction between the surfaces and the fluid that circulates in the space between the rotor and the stator of rotary electrical machines.

[0002] This situation worsens as the rotation rate of the machines rises.

[0003] Accordingly, it is necessary to provide a cooling system which is capable of dissipating the generated energy and of ensuring that the maximum temperatures reached by the rotor and the stator are such as to avoid degrading the electromechanical performance of the materials that are typically used.

[0004] For example, for a permanent-magnet motor the permanent magnets must not reach excessively high temperatures, on penalty of losing or degrading their magnetic properties.

[0005] The system must also typically work within clearly defined temperature values which are generally rather low in order to have low costs.

[0006] The heat exchanger must also be compact and highly efficient.

[0007] The problem of removing the heat generated by an electrical machine is currently dealt with in various manners.

[0008] The main technique consists in using fins which are struck by a stream of air generated by a fan and are arranged on the shell of the machine or inside it according to the various configurations.

[0009] When a fluid is used for cooling, the motor is enclosed with a jacket inside or outside which the fluid is made to pass through appropriately shaped passages. Cooling can affect both the stator, as is usually the case, and the rotor, and in this case cooling generally occurs by means of a static exchanger arranged around said rotor.

[0010] The effectiveness of the exchanger is more important in high-speed machines whose dimensions must be compact and in which accordingly the dimensions of the auxiliary components, such as the heat exchanger, cannot exceed certain values.

[0011] Two kinds of heat exchanger are generally used in conventional electrical machines.

[0012] A first type has a constant cross-section, in which the flow is generally laminar. In order to increase the efficiency of this heat exchanger, it is necessary to increase the speed so as to produce turbulent motion conditions. This entails a significant increase in pressure losses and entails higher pumping costs.

[0013] A second type is the one in which the motion is rendered turbulent by inserting appropriate obstacles. This solution has the advantage of increasing heat exchange efficiency for an equal flow-rate of the cooling fluid. Despite the fact that the presence of obstacles increases pressure losses, accordingly requiring once again to use pumping elements capable of propelling the fluid under high pressure differentials, this solution is generally more efficient than the preceding one.

[0014] The aim of the present invention is to provide a forced-convection heat exchanger for rotary electrical machines which is highly efficient and capable of removing the considerable thermal energy levels generated in the stator and rotor elements of the electric motor.

[0015] Within the scope of this aim, an object of the present invention is to provide a forced-convection heat exchanger which is particularly compact and therefore suitable for electric motors which are compact but have a high specific power level.

[0016] Another object of the present invention is to provide a forced-convection heat exchanger for motors which allows to remove heat from the regions of the electric motor where it is generated most.

[0017] Another object of the present invention is to provide a forced-convection heat exchanger which allows to keep the temperature of the inner face of the stator, which is the most critical one, at an acceptable level in accordance with the characteristics of the materials used.

[0018] Another object of the present invention is to provide a forced-convection heat exchanger which also allows to maintain low temperatures on the surface of the rotor.

[0019] Another object of the present invention is to provide a forced-convection heat exchanger which is highly reliable, relatively easy to manufacture and at competitive costs.

[0020] Thus the present invention provides forced-convention heat exchanger for a rotary electrical machine, comprising one or more tubing elements, that are arranged between the conductors of the stator windings of said rotary electrical machine, so as to be in contact with the outer surface of said conductors, a cooling fluid flowing into said tubing elements.

[0021] Further characteristics and advantages of the present invention will become apparent from the description of preferred but not exclusive embodiments of the heat exchanger according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein:

[0022]FIG. 1 is a partial schematic plan view of a first embodiment of the heat exchanger according to the present invention; and

[0023]FIG. 2 is a partial schematic plan view of a second embodiment of the heat exchanger according to the present invention.

[0024] With reference therefore to the above cited figures, in which identical reference numerals designate identical elements, the heat exchanger according to the present invention is provided as follows.

[0025]FIG. 1 is a view of an embodiment of the forced-convention heat exchanger according to the present invention, in which the reference numeral 1 designates the portion of the stator core of the rotary electrical machine. The reference numeral 2 designates the conductors (for example made of copper) of the stator windings of the rotary electrical machine.

[0026] The forced-convention heat exchanger comprises one or more tubing elements 3 which are arranged between the conductors 2 so as to be in contact with the outer surface of the conductors 2.

[0027] A cooling fluid flows into said tubing elements that, in a preferred embodiment of the present invention, are connected to collector means (not illustrated) for collecting the cooling fluid circulating into the tubing elements 3.

[0028] The collector means comprise preferably a first collector element and a second collector element that can be respectively connected to a first end and a second end of said tubing elements.

[0029] Said first and second elements are preferably made of non-conductive material such as for example polyketon or polysuplfone resins. In this way the circulation of eddy currents is avoided, with a remarkable reduction of the dissipated power.

[0030] Preferably, the heat exchanger, according to the present invention, comprises pumping means (not shown) which, being operatively connected to said tubing elements 3, ensure forced convection of the cooling fluid.

[0031] According to a first embodiment, the tubing elements 3 of the heat exchanger are arranged, so as to be aligned with the conductors 2 longitudinally along the body of the stator core.

[0032] According to this embodiment, by means of the action of the pumping means the cooling fluid enters proximate to one end of the stator core and exits at the opposite end, in practice passing only once at the stator region to be cooled.

[0033] According to an alternative embodiment, the tubing elements 3 of the heat exchanger are arranged in a coiled configuration longitudinally along the stator body. According to this embodiment as well, the main axis of the tubing elements is parallel to the conductors 2.

[0034] Also according to this embodiment of the present invention, the cooling fluid can be pumped at one of the ends of the coil and in practice multiple passes of the fluid occur at the stator region to be cooled.

[0035] According to another embodiment, the tubing elements 3 of the heat exchanger are coupled to the conductors 2 so as to follow their path around the stator core. In practice, the tubing elements 3 can be coupled to the conductors 2, for example by means of banding insulation, and then wound around the stator core together with the conductors that constitute the stator windings.

[0036] By using the described configurations, the tubing elements 3 can be arranged proximate to the surface of the stator that faces the rotor, as shown in FIG. 1, or be fully inserted between the rows of conductors 2, as shown in FIG. 2.

[0037] The proposed solutions allow to remove heat where it is generated and also allow to provide a temperature level on the face of the stator that faces the rotor 4 which allows to maintain lower temperatures on the rotor than obtainable with conventional solutions.

[0038] Furthermore, the heat exchanger, according to the present invention, is extremely compact and can therefore be used even for compact electrical machines having high specific power levels.

[0039] The tubing elements 3 of the forced-convention heat exchanger, according to the present invention, can be made of metallic material, so as to facilitate optimum thermal contact with the surfaces to be cooled, or of electrically non-conducting material, such as for example PTFE (polytetrafluoroethylene).

[0040] As an alternative, it is possible to provide tubing elements 3 which have a configuration other than the circular one shown in FIGS. 1 and 2 and can be such as to substantially fill the stator 1.

[0041] In practice it has been observed that the forced-convention heat exchanger, according to the present invention, fully achieves the intended aim. In fact, it allows maximizing heat exchange efficiency by eliminating heat generated at the interface between the stator and the rotor of an electric motor, though being compact and therefore suitable for use in electrical machines in general having a high specific power level, including compact ones.

[0042] The heat exchanger thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; all the details may furthermore be replaced with other technically equivalent elements.

[0043] In practice, the materials employed, so long as they are compatible with the specific use, as well as the dimensions, may be any according to requirements and to the state of the art. 

1. A forced-convection heat exchanger for a rotary electrical machine, comprising one or more tubing elements that are arranged between the conductors of the stator windings of said rotary electrical machine, so as to be in contact with the outer surface of said conductors, a cooling fluid flowing into said cooling elements.
 2. A forced-convection heat exchanger for a rotary electrical machine, according to claim 1, characterized by the fact that said one or more tubing elements are operatively connected to collector means for collecting said cooling fluid flowing into said cooling elements.
 3. A forced-convection heat exchanger for a rotary electrical machine, according to claim 2, characterized by the fact that said collector means comprise a first element and a second element that are respectively connected to a first and a second end of said tubing elements.
 4. A forced-convection heat exchanger for a rotary electrical machine, according to claim 3, characterized by the fact that said first element and said second element are made of electrically non-conducting material.
 5. A forced-convection heat exchanger for a rotary electrical machine, according to one or more of the previous claims, characterized by the fact that said one or more tubing elements are operatively connected to pumping means which are suitable to ensure forced convection of said cooling fluid.
 6. A forced-convection heat exchanger for a rotary electrical machine, according to claim 1, characterized in that said tubing elements are arranged proximate to the surface of the stator that faces the rotor of said electrical machine.
 7. A forced-convection heat exchanger for a rotary electrical machine, according to claim 6, characterized in that said tubing elements are aligned with respect to said conductors longitudinally along the body of the stator of said electrical machine.
 8. A forced-convection heat exchanger for a rotary electrical machine, according to claim 6, characterized in that said tubing elements are arranged in a coil-like configuration longitudinally along the body of the stator of said electrical machine.
 9. A forced-convection heat exchanger for a rotary electrical machine, according to claim 8, characterized in that said tubing elements are coupled to said conductors along the path around the stator core of said electrical machine.
 10. A forced-convection heat exchanger for a rotary electrical machine, according to claim 9, characterized in that said tubing elements are coupled to said conductors by means of banding insulation.
 11. A forced-convection heat exchanger for a rotary electrical machine, according to one or more of the preceding claims, characterized in that said tubing elements are made of metallic material.
 12. A forced-convection heat exchanger for a rotary electrical machine, according to one or more of the claims from 1 to 10, characterized in that said tubing elements are made of electrically non-conducting material.
 13. A rotary electrical machine characterized by the fact of comprising a forced-convention heat exchanger according to one or more of the previous claims. 